Harvin was nearly all Pete, IMO. Pete drooled over his specific talents, and had been since USC.
If John failed, it was in the background/character evaluation part. However, I believe Pete essentially overrode John in that area. I think Pete lobbied John that Pete was sure he'd be successful with his Boystown Father Flanagan reclamation project on Harvin. He was just another misunderstood young African American man, and another Marshawn Lynch success story just waiting to happen, and besides, the increasing success of the Bruce Irvin reclamation (from the streets) project was showing Pete's Midas touch; hey, Pete's as good as a sure thing on these.
Except that Harvin's problem is a mental illness, an internal way of being that is far stronger than Pete's "team culture", and in fact is nearly guaranteed to be a turd in the punch bowl of that culture. I believe Percy Harvin shows all the signs of Borderline Personality Disorder, and that explanation perfectly matches Harvin's entire history and trail of incidents and issues. Once Pete and John realized what they were actually dealing with and got professional advice, they dropped Harvin like a hot potato. They will not make that mistake again. Search my other posts on "Borderline" and "Harvin" for a more detailed breakdown of the condition and a play-by-play breakdown of how I believe that played out with the Seahawks. I expect Harvin will be on his best behavior with New York probably until the middle of next season, and then the mask will come off.
If someone has quality information that more clearly shows John's role in the Harvin fiasco, even (especially) if it differs from my take, please share it; I'd love to see it. Mainly I recall Pete talking about how they graded Harvin as a first-round talent for the current draft class, and it made more sense to go with that than to take a chance in the draft.